1. Field of the Invention
This invention relates to lathe-type machine tools for machining cylindrical or tubular workpieces.
2. Description of the Prior Art
Lathe-type machine tools adapted to remove material from the periphery of cylindrical or tubular workpieces, including inner and outer peripheral surfaces as well as end surfaces, are generally known in the prior art. They are useful for cutting, beveling, shaping, counterboring and similar machining operations on cylindrical or tubular workpieces, in particular, metallic pipe and tubular stock articles. Machine tools of this type are adapted to be secured on the workpiece itself or the workpiece can be secured relative to the tool by a suitable work holding arrangement. If the tool is attached to the workpiece, it is conventional to use a mandrel or clamp to secure the tool on the workpiece. If the workpiece is secured within the tool housing, the tool itself is usually provided with a suitable centering and clamping arrangement to locate and secure the workpiece at an appropriate position within or on the tool to enable an operator to carry out a precision machining operation on a surface of the workpiece.
It is also conventional in the prior art to construct tools of this genre so they can be divided along a transverse centerline to enable the tool to be opened and then placed around the periphery of a continuous tubular or cylindrical workpiece to enable the tool to be utilized on a continuous length of tubing or pipe without cutting the latter. In typical prior art applications, it is conventional to drive the cutting bit of the tool in an orbital path about the centerline of the tool in a cutting plane that may be selectively advanced axially, depending upon the machining operation to be performed. If the workpiece is to be radially cut or grooved, for example, the tool may perform its cutting operation in a single plane, the plane of the cut or the groove, without any requirement to axially feed the cutter except to precisely locate the cutter at the desired area on the workpiece where the cutting operation is to be performed. On the other hand, if the workpiece is to be machined along an axial portion thereof, it is conventional practice to provide means to axially feed the cutter along the length of the workpiece to thereby move the cutting plane axially along the centerline of the workpiece while the cutting operation is being performed.
While it is the more usual practice in connection with tools constructed in accordance with the above description to drive the cutter around the periphery of the workpiece (around the longitudinal axis of the tool), it is also well-known to hold the cutter at a fixed position while the workpiece is rotated relative to the centerline of the tool, with or without relative axial motion between the cutter and the workpiece. The selection of the design of a particular tool may depend upon the relative sizes of the tool and workpiece and upon the environment in which the machining operation is to be performed.
Whether the cutter of the tool is driven around the workpiece or is held fixed while the workpiece is rotated, it is also known to arrange the cutter to follow the periphery of the workpiece where the workpiece is non-symmetrical around its longitudinal axis. In these circumstances, it is desirable that the cutter be allowed to move relative to the rotary axis of the tool so that it can follow the surface of the workpiece (for example, the inner or outer peripheral surface of a tubular workpiece) rather than a fixed reference axis. Tools of this type will usually include a roller or guide in contact with the surface of the workpiece, with the guide arranged to precisely follow the workpiece contour in the cutting plane of the tool. Usually, the guide is a roller element and is connected to the cutter bit of the tool by an appropriate linkage that enables the cutter to follow the motion of the roller so that the reference point for the cutting operation is the position of the roller as it follows the surface of the workpiece. Cutting tools of this latter variety can be referred to as having a "floating head", with reference to the cutting head which can be envisioned as "floating" around the longitudinal axis of the tool as the cutter and workpiece are relatively rotated around the longitudinal centerline of the tool system.
Specific examples of such "floating head" lathe-type machine tools arranged to perform various cutting operations on tubular workpieces can be observed in U.S. Pat. Nos. 2,842,238, 3,608,406, 3,733,939, and 3,942,248. It will be noted from observing the aforementioned patents that the usual objective of using a floating head in tools of this type is to enable the cutter to follow an eccentric or irregular workpiece while still performing a cutting operation that is uniform along the surface of the workpiece. However, a specific problem that is not seen to be addressed in the prior art concerns the removal of an axial irregularity from the surface of a workpiece by utilizing a floating head, for example the removal of the peripheral crown of a weldment between sections of pipe that have been butt welded together.
Removal of a surface irregularity from tubular workpieces that are perfectly aligned on opposite sides of the irregularity normally would not present any problem for lathe-type machine tools that are known in the prior art. Either a floating head or a fixed head could be used to remove such irregularities by simply axially advancing a cutter along the surface of the workpiece from an axial side of the irregularity to the other side. However, it is rare that the two sections of the workpiece on opposite sides of a weldment are perfectly aligned and symmetrical with each other, and this situation creates a special problem when it is desired to remove the crown of a weld without removing substantially any base metal of the workpieces welded together. It will be recognized immediately that axially feeding a cutter along the workpieces, even with a floating head, cannot be utilized where the workpieces on opposite sides of the irregularity are not precisely axially aligned. A conventional floating head will need to follow either one side of the workpiece or the other, but cannot follow both sides simultaneously.
Prior art lathe-type machine tools, even tools utilizing various forms of floating heads, are incapable of removing peripheral irregularities from cylindrical workpieces, where the peripheral surfaces of the workpiece are not concentric and generally symmetrical on opposite sides of the irregularity. The present invention has for its primary objective and purpose the removal of an axially extending peripheral irregularity from a workpiece that has radial eccentricity on opposite sides of the irregularity. It is distinguishable over all prior art tools in that the cutter of the tool constructed in accordance with this invention can be axially advanced along an imaginary reference line connecting two axial reference points located on the periphery of the workpiece on opposite sides of the irregularity, all while the cutter is advanced around the periphery of the workpiece in a floating head system.